Pulse code translator



Sept. 2, 1952 Filed Jan. 7, 1950 A. I EsTl 2,609,529

PULSE CODE TRANSLATOR 3 Sheets-Sheet 1 ATTORNEY Sept. 2. 1952 A. LES-n2,609,529

PULSE CODE TRANSLATOR Filed Jan. '7, 1950 3 Sheets-Sheet 2 ,v vo.' vv vvvvv v. v.' vvv VN 3.9 E A coo/N6 v c/fcy/f non 00%: 4

INVENTOR /J/P/vow L55 r/ ATTORNEY Sept. 2, 1952 A. L EsTl 2,609,529

PULSE CODE TRANSLATOR Filed Jan. 7, 1950 3 Sheets-Sheet 3 TIME DEL/1 Yim l INVENTOR ,4F/vow fsw SYM@ ATTORNEY Patented Sept. 2, 1952 PULSECODE TRANSLATOR Arnold Lesti, Nutley, N. J., assigner to Federal`Telecommunication Laboratories, Inc.,

New

York, N. Y., a corporation of Delaware Application January 7, 1950,Serial No.`137,392

18 Claims. l

This inventionlrelates to'pulse'code translators andmore particularly toa system for translating pulsertime modulation signals into pulse codemodulation signals.

Systems Lknown generally as hpulse code modulation systems arebecomingincreasingly important for use .in communication; In Athesesystems signal energy istranslated into-pulse codecombinationsfrepresentative of fadiscrete number of signalvariations',these code combinations being later `decoded to reproduceeiectively the.orig;- inal signals. v.In pulse code systems so far proposed 'e'quipmentis provided Yfor 'obtainingmeasurements of amplitude 'of discretesignal'portions, theseamplitude measurements `being translated invarious pulsev code combinations. The ar"- rangements for establishingthe .discrete amplitude'flevels from a signal wave are generallyreferred vto as quantizers and 'a `number of different quantizers andcoding 'circuits for the translation of amplitude modulations 'intocodes have been heretofore proposed.

'It is an object of this invention to provide a system for translatingsignals `represented as timefdisplacements of pulses, generally referredto as fpulse time'modulation or PTM, vinto pulse code combinationsreferred to generally as pulse code modulation or PCM signals.

In'laccordance withthe invention there is provided a'plurality ofnormally blocked coding cir-'- cuits 'and rstand second-pulse sources,the pulse fromy one of these sourcesbeing vtime modulated. Pulses fromone of thesesources are'sequentially applied to the coding circuit tocondition them for release in different combinations Yrepresentative ofthe different code signal combinations indicating signal amplitudes andthe pulses from the other lpulse source are applied also to the codingcircuits related in time with the time modulation so that pulses may bereleased from these circuits in combinations corresponding to the pulsetime modulation signals.

According to'a feature of my invention the pulse coding circuits maytake the form of coding tubes or other rcoding circuits. Either the timemodulated pulses or other pulses related by an integral multiple,including unity, of thepulse repetition rate of the time modulatedpulses, are applied to the coding circuits in time displaced fashion sothat the coding circuits 'are' sequentially conditioned for conduction.lPulses from la second source are then applied to'these coding circuitsso that in the circuits wherein both pulses are present conduction willoccur. Thus there will be in the output of the tubes `pulsescorresponding to 'a predetermined code. By means of some distributornetWork'these pulses may be applied to a common transmission medium as apulse code combination representative of the particular time modulatingsignal. Either the Mpulse time modulated signals or the other pulses'may be applied through the' time distributor to the tubes, the pulse ofthe other source servingV to trigger the tubes into operation.

In one formof my 'inventiona vdelay means is provided which mayconstitute a single delay device or aA plurality of delay devices, thetotal delaying action corresponding substantially to the maximumftimedisplacement which the time modulated pulse undergoes. These delay meansare coupled `in different code combinations to separate ones of thecoding tubes so that all of the coding combinationsof the particularcode in use will be sequentially established at the'coding circuits. Theother pulses then are applied to gate these tubes at a time when thedistribution corresponds to the code indication allotted to a particulartime position of the time modulated pulse. With this system any type-ofcoding may be used, for example, the usual-binary permutation coding,cyclic permutation'c'oding or any arbitrary form of coding.

In accordance with a secondembodiment of my invention one of said pulsesources may comprise an arrangement `for applying to different codingcircuits different coding pulse waves related in a `series inaccordancewith the code combination to be used. The pulse time modulatedenergy is synchronised With the production of these coding pulses and isapplied simultaneously to the coding gate circuits so that pulses willbe released from these circuits corresponding to, the particularvoltagev condition of each of these circuits at the time the timemodulated pulse is applied.

The above-'mentioned and other features and objects of' this invention'and the manner of attainingthem will become more apparent and theinvention itself will be best understood by reference to the followingdescription` of an embodiment of the invention taken in conjunction withthe accompanying drawings, in which Fig. 1 shows a set of graphsexplaining two known types of code combinations;

Fig. 2 is a schematic circuit diagram illustrating the principles of myinvention applied to one type of binary code translator system;

Fig. 3 is a set of graphs used in explaining the system illustrated inFig. 2;

Fig. 4 is a modification of a portion of the illustration of Fig. 2showing a cyclic permutation code combination;

Fig. 5 is a modification of the circuit such as shown in Fig. 2illustrating a method for volume compression utilizing a system of thisinvention;

Fig. 6 is a graph illustrating a volume compressor action of the circuitof Fig. 5; and

Fig. 7 is a still further modification of a circuit incorporating thisinvention.

In a standard ve unit code there are provided 32 signal unit levelsextending from zero to 31. Accordingly in the description which followsthe reference numerals 0-3I will be utilized to indicate these codingpositions or corresponding amplitude variations of such signals. Turningnow to Fig. 1, there is illustrated adiagram forexplaining the operationof establishing a threeunit, eight-level binary permutation code inaccordance with graphs A, B and C and the corresponding three-unit,eight level code of a cyclic progression or permutation code asillustrated in graph D, E and F. The eight signalV levels are designatedby reference numerals il, l, 2, 3, il, 5, E, and l. In the three-unitbinary permutation it will be noted that in graph A the signal is onevalue, for example, zero for reference level zero and a second level forI. This graph continues on with the first value for Zero and all eveninteger references of the code and a second level for i and all oddinteger references of the code. For the second code element graph, Bshows that the signal is then maintained at the first condition for thefirst two amplitude reference levels, changes to the second conditionfor the next two amplitude reference levels, reverts to the firstcondition for the next two and repeats this cycle throughout. For thethird signal element graph C shows that the first-condition ismaintained for the iirst four amplitude reference level conditions,changes to the second for the next four and so on. If additional signalelements are provided these again will be arranged so that the firstcondition exists for the first two changes of the next precedingvcodeelement and then changes for an equal number of code positions. This isthe standard binary permutation coding and it is believed no furtheexplanation is required.

For the cyclic permutation coding it will be notedthat the graph Dremains in the initial condition for the rst coding level, changes tothe second condition for the next two, `returns to the first conditionfor the succeeding two, Aand so on. In graph E the second codingelementremains at the first condition to the mid-point of the portion of graphD in its second condition, then changes to its second condition andremains there to the mid-point of the succeeding similar portion ofgraph D. Graph F again changes from the first to the second condition atthe mid-point of the second portion of graph F and so on. Thus if therst condition is described as the spacing condition and the second asmark condition it will be seen that code combinations are set up formark and space for each of the various levels to zero through 1 indifferent combinations for the two types of coding. It will be clearthat other types of arbitrary coding may be adopted for transmitting ofsignals by codes but these two being the most prominent have been mostthoroughly described.

With this explanation we turn now to Fig. 2 which illustrates anembodiment of my invention exemplied in a seven-level, three-unit binarypermutation coding translator. A plurality of coding circuits includingtubes 32, 33 and 34 are provided, these tubes being biased so asnormally to be blocked for the passage of energy. To each of tubes 32,33 and 34 are coupled coding lines 35, 35 and 31. A delay line 33terminated in a -resistor 39 is provided to which are connected at equalspaced tapped points, corresponding to the levels zero through 6,individual contacts 43, 4l, 42, .43, lill, 45 and 56. Pulses from apulse generator d1 may be applied to traverse along delay line 38, overswitch i3 in its position as shown. A second pulse source is shown at49, this source being 'a source of time modulated pulses. These pulsesare applied over a switch il and line 5l to all of the code transmittertubesZ-,Sl-l in parallel. Tubes 32-3ll are so biased that the'blockingwill not be released except-by simultaneous application of pulses fromline 33 and line 5| thereto. At the time that simultaneous applicationof pulses does occur there willappear in Athe separater output lines 52,53 and 54 pulse signals consisting of pulses representing vthe two codeconditions Vof the code transmitter arrangements in a Aparticularcombination. These' pulses may be applied over the distributor 55 to acommon outputmediumi. Distributor `535 may be any type of distributor,for example it may consist of delay lines of different Value or may beany type of cyclic mechanical or electronic'distributor. The separatelead lines 451-46 are coupled by meansof-resistors 5l, to differentonesof the coding lines 35, 36, 37 so as to establish sequentiallythrough the operation of the` delaydevice 38 different code combinationson the coding tubes 32,-34. Preferably the pulses from generator 47'have `a time duration substantially equal to fractional unit of thetotal time displacement of the time modulated pulses andthe delaybetween lines 40, lli, etcfis so chosen :thatthis delay is alsosubstantiallyequal to the timeV duration of these applied pulses. Thusthere will be a continuity of the code scanning as sequentially appliedto tubes 32, 33 and/34. The time modulated pulses from the output ofpulse time modulator 43 will appear at different times depending uponthe degree of modulation so that the tubes will be triggered into actionat the time corresponding to the particular time displacement and codepulses will therefore be established corresponding to this level.

If desired switches A13 and 5t may be changed in position to their lowercontacts thus applying the time modulation pulses from source 49 tordelay line S3 and the regularly spaced pulses from generator il totriggering line El. The two sets of pulses kwill thus establish the codetranslation asr previously described.

Referring to Fig. 3 a clear understanding of the operation of the Systemmay be had. In this figure the ordinates represent amplitude and theabscissae represent time. In this figure graph G represents 0, I, 2, 3,4, 5, and 6, the successive time positions of a pulse 58 midway overveachof the corresponding positions 0 5 shown 5.5.1 in'Fi'g: 211':GraphH represents 1a.modulated pulse 5 9 fin each ..ofits-corresponding: time y-ipositionssll 1. throughlIi-"representings-the modulation :valuesof' the signal Asfshown'-.this=pulse 591isiinfinstane.-

taneoustime.'l positionf representing :forfexam ple zel-'of` modulation.level midway Jof4 its @maximum and minimumfswingll.thuscorrespondingftofposb tion 3 in the coding circuit ofFigf; 2;#Inzthe.`

binarycode: of glii'g..` .2.this :will be; amariti-markspacen=indicationx as set: up in-fthe.`l coding; tubes.32--34 so that there will be two.'outputzfpulses.at4`

this."codingposition.;r In graphssJ; Kand L .of Fig: 3 'ztherefis shownrespectivelyztheapulse.v 5 9 in four different i modulation positions:correspond-1. ing-.to positions;.4,"2fand 5irespectivelynof ftheK-:iillustrates:A the.`

coding connections in Figi-2:1 corresponding coincidence;-timingfoftftheepulses responding to: time 'modu-latedpulses :5Sisbeingain-g dicated by a heavier line. In graphL areashown puls'ezcode. combinations i605 representativefofthevariousscodeapositions.offithe, pulsetime. moduf lated'wave;A

It v.will beissen :fromnth'erabove vexplanation that the.y circuitfoffFignZ' vwill .iserveto ztranslate: pulseV time :modulated energy-f-from modulator.` 49 finto. thedesiredl pulse.codecombinations:..Whilethe circuit tof i Fig; 2 .has been shownby yway .of ex ample asapplied to a simple three element code it .willibe yunderstood Ithatithis may be.- expanded towcover for` usef -in any .f multielementzcode f dependent f.upon the1.;numb'er of I amplitude levels necessaryforv carryingv anzintelligible. signal.,. For i speechit fis clear :that:morefthan-fthe vseven levels r illustrated mayzrberequired.y I Underthese cire cumstances a 5, 6 or even higher unit codemay be used:`

In Fig:-` 4` is shown; a accede f conductor 'l system.v

substantially to: that of fFig; 3.-.but:connected for transmission of.aLterr-leveLfour-unt cyclic vpro- In this connection thereareprogression code. videdten tapping; points on4 delay. line. 38y andtapping.. points from fdelayxmeansv 1.38are-fcoupled th-roughgcouplingi4 resistors .65.5 to: the: separate coding yconductors .l I-`64the. cyclic .permuta-e. tioncode combinationsrepresenting.:thes 0 to II0i amplitude levels;A It 4is understood that zwith' the f four-unit`code.- upzto: -16.f amplitude; levels.- could bezprovideds vThecoding:operationrproceeding. for rthe .cilcuitfof` FigtAa is:identicalwith .that described f in :connection .with Fig," .2t so. ittwill not" be repeated indetail. here.y

It :will be: understood :infconnectionzwith both these'y illustrations.thatf: a singled delay line aas.- shown :at 38.'neednotrbaprovidedfsincethe same time. distribution could: beobtainedby: individual fdelay;ylines: or "other delay,l devices-each: havin-g.

delay .f values Vcorresponding* to` Vtheesectionsaoii through 6 .Iinclusive. Thisv has f not been I ill-ustrated. since i the :simpler:form. showny vin these.

Itzwill likewise.

iigures lis generallyl` preferable. be .clear :that also: any1arbitrarypcodermaylbe ese tablished-by lconnection iof the;variousfdelay line i portions .tofdifferent'zonesothescodingiconducftors in any arbitrary-manner.;desired 'Ihis'sys--` tem; is. therefore;Vextremely flexible: as: any de.-

sider arbitraryrcode combi-nation' canfbefsused, al'.

though in general :practiceonezof ithemore 'usual forms wouldlikely'beadopted?y VolumeV Y compressionnor expansion may be achieved .With` thesystem, as hereinzdescribedsby..

effectively changingftlreetappingf points .on re.-

sistor 38:as,desired;.V An illustration offthis'formandivolumetcompression is.` given in Figse tand f6' wherein.the;coding..circuitisfshownfor a132-flevel,v 5eelement... loi-naryIpermutation code.y In this figureethe. z delay lineV 138;: is' shown Iprovided fwith regularly y:spaced taps `Il'through'v 3 Iv inclusive.

In-f.-Fig.-6 therefisil1ustrated the stepped curve feach step of. whichrepresents oneL ofthe amplitude Klevels .i fromy zero to v3 I. that.the-'zero signalmodulation level will then bel at..level I 61asindicated bythe-'dot dash .linel Rfeverting v'to Fig.i5 ithe ve coding:conductors are shownfat 68, 69;.701," Hand-'I2 respectively.v

The tappingpoints corresponding to energy levelsv -8; 9arefinter-connected and arecoupledto lines 68S and-2li to` establish thecode combination corresponding foramplitude level 9 for both tappi-ngpoints 8 and Il.v Tappingpoints 5,16, I 'are-inter connected 'andconnected tovcoding conductor 68 and 69 "tof establish a code-levelcorresponding to that-normally representedat coding --position 8A andtapping apoints 0-'4-' areinterconnected vand connectedto codingleads-69" and Iii-toestablish acodringflevel corresponding to the normalcoding level at tapping point-vl. It willthus bek seen rthat Lin thenegative swing ofthe time-modulatedpulses the-coding'swing Will onlygo'from level I6 down to level-1; thus accomplishing a volumecompression for this --negative swing. Similarly-at the lupper endor-positive PTM vswing tapping points 23,1 24 are connected together andconnectedl-to'codi-ng lines- 68",- 10 and-'I2 to establish the normalcoding connections for `tapping point-IIB.AV Tappingjpoints 25 to2"I"are interconnected and connected 'ton the `codingiconductor 'I2 toestablish ther code connections normally provided; forat level 23, and`tapping points 1 28e-3 I-4 are `rinterconnected l and connected 4to lthecoding conductors 68; 169, III;V 'I I `and "I2 'to' establish the fnormal 'coding level for coding position 25.- Thus atthe positive'end ofthePTM sweep theJL codeleve1` in -between'- I 6 and level-25, thuscompressing the-signal fon' this Yside. The Variation provided' inthe-step wave of-SB is indicated by dotted-lines 68-and 69,'Fig; 6.

Whilel code translators *utilising the delaymeans-'distributorarrangements as shown in theA foregoing gures have theadvantage of complete ileXibility-otcode-in some instances it may bedesirable-to utilizeadifferent typeof systemoperatesfzatf.a.'` frequencyequal toa multiple,

ofi? the: normally'. unmodulated spacing.v position ofthe time..lmodulated pulses from pulse time modulation `source I4; Output. energy.from this oscillator:v iswapplied: togav clipper amplifier 'I5which',-serves` to;V clip the .f sine Wavek oscillations fromIf3.:;a:u;dj,amplify-themr toy provideA a series ofcoding-,pulsesfI6z1corresponding to those of graphsA'xor vD of` Fig.v L.The output.: from clipper amplier'15lis applied to coding tube 32;

and ithrough'coupling, circuit 'II to arst trigger.

circuit I8 which may be what is known yasi'flip- It will be Y clear Inthis connecting 7 ilop circuit or a trigger circuit of the Eccles-Jordan type, in which circuit changes from one stable condition to asecond stable condition in response to each applied pulse. Thus outputwave 'I9 is produced in line 33 corresponding to graphB or E of Fig. 1.In order to obtain graph E of Fig. 1 coupling circuit 1l must include adelay circuit or a delay circuit must be inserted in line 35 so that thepulses of 19 will be initiated midway of pulse 'H of Fig. l. The outputWave 'I6 is applied to coding circuit 33 and over coupling circuit 8G toa second iiip-op circuit '8l Which may be identical in form to thatdescribed in connection with 1S. The output of flip-flop 8l will be apulse 82 corresponding to the pulses shown in graph C or` F of Fig. 1.Here again the delay provisions in coupling circuit or in line 31 mustbe provided if the system rfor graph F is to be obtained. Pulses 82-havethe same repetition rate as time modulated pulses S3 from pulse` timemodulator 74. These pulses are appliedrto coding .circuit 3:1 whichv mayalso be Vapplied through a coupling circuit 84 and line 85 tosynchronise pulse time modulator source 'ld so that the time modulatedpulses are properly synchronised with the coding Waves 'i6-'82. It willbe evident that as Waves "i5, 79 and 82 are successively applied to thecoding circuits 32, 33 and 34 respectively its circuits will besequentially conditioned for release at diner-ent positionscorresponding to the eight coding levels of the system. Accordingly,when the pulses 83 from modulator M are applied to these coding circuitspulses will be released through the. output lines 52, 53, 54 into propercoding position to correspond with the coding combinations for theparticular amplitude level related to the pulse time modulation. Thiscircuit may be desirable in many applications since it may be designedwith only the number of flip-nop circuits corresponding to the variouscode elements andA does notrequire individual delay devices for each ofthe amplitude levels to be taken care of. From the above description theoperation of the systemin translating time modulation into pulse codemodulation is believed to be clear.

It will be understood that while a few examples .have been given hereinof the particular coding circuits the principles of the invention willbe readily adapted for application to other types or" coding systems andcircuits without requiring inventive skill.

While I have described above the principles or" my invention inconnection with specic apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention.

What I claim is:

l. A system for translating pulse time modulation signals into pulsecode modulation signals comprising a plurality of normally blockedcoding circuits, a rst pulse source, a second pulse source, the pulsesof one of said sources being time modulated, means for sequentiallyconditioning said coding circuits for release in different combinationscorresponding to the different code signal amplitude levels undercontrol of pulses from said first source and means for releasing saidcoding circuits under control of pulses from said second source inaccordance with the time modulation of said pulse time modulationsignals to provide corresponding code combinations.

2. yA system according to claim 1, wherein said means for conditioningcomprises successively valued delay means coupled to said rst source andto selected ones of said coding circuits.

A3. Av system accordingfto claim 2, wherein said delay means comprises acommon delay line, provided with spaced tapping points for coupling tosaid coding circuits.

4i. A system according to claim 3, wherein said tapping points arespaced to provide substantially equal delay periods;

5. A system according to claim 4, wherein said iirst pulsesourcecomprises a sourcer of pulses having a repetition ratesubstantially equal to the repetition rate of the unmodulatedpulses fromsaid second pulse source.

6. A system according to claim 5, wherein said rst pulse source providespulses having a duration substantially equal to the time delay betweensaid tapping points. j

7. A system according to claim, wherein said iirst pulse source iscoupled to said delay means.

8. A system according to claim 1, wherein said nrst'source comprises asource of time modulated pulses of a given repetition rate, and saidsecond source comprises a source ofpulses related to the pulses fromsaid first source as an integral multiple including unity of saidpredetermined rate.

9. A system according to claim 8, wherein said second source comprises aplurality of pulse producing means individually coupled to said codingcircuit, one of said pulse producing means operating at saidpredetermined repetition rate, and

the others at successively higher harmonics thereoi.

lil. A system according to claim 8, wherein said second source comprisesa source of pulses having a repetition rate substantially equal to theunmodulated repetition rate of said time modulated pulses.v

l1. A translator for translating pulse time modulation' signals intopulse code `modulation signals comprising a rst source of pulses havinga predetermined pulse repetition rate and a predetermined modulationtime displacement representing amplitude levels of a modulating signal,a second source of pulses having a repetition rate related as anintegral multiple including unity of said predetermined repetition rate,a predetermined number of normally blocked coding circuits releasableunder control of simultaneous applica- 'tion thereto of pulses from bothsaid sources, means for applying pulses to respective selected ones ofsaid coding circuits from one of said sources in different combinationscorresponding with a predetermined number of different signal amplitudelevels and means for applying pulses from the other of said source toall said coding circuits.

12. A translator according to claim 1l, wherein the repetition rate oisaid pulses is substantially the same as said unmodulated repetitionrate, said pulses eachhaving a duration corresponding with the timedisplacement of said modulated pulses representing signal amplitudeswithin the corresponding amplitude level.

13. A translator according to claim 12, wherein said rst source iscoupled with said means for applying pulses to said coding circuits.

14. A translator according to claim 12, wherein said second source iscoupled with said means for applying pulses to said coding circuits.

15. A translator according to claimll, wherein said means for applyingpulses comprises delay i() the signal amplitudes as applied to saidcodin circuits.

ARNOLD LESTI.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS 10 Number Name Date 2,403,561 Smith July 9, 19462,429,616 Grieg Oct. 28, 1947 2,485,591 Grieg Oct. 25, 1949

